1. Technical Field
The present invention relates to a printing apparatus and a printing medium conveying apparatus that print any predetermined text, images, and others or a printing medium by forming minute particles (dots) thereon through ejection of a small amount of liquid from a plurality of nozzles.
2. Related Art
With the reason of the relatively inexpensive price and the ease of achieving high-quality color printing, an inkjet printer being an example of such a printing apparatus has become widely popular not only for office use but also for personal use with the spread of personal computers, digital cameras, and others.
Such an inkjet printer generally creates any desired printed matter with minute ink dots formed on a printing medium. More in detail, a moving element referred to as carriage or others includes an ink cartridge and a printing head (liquid ejection head) as a piece. Such a moving element ejects a liquid ink from a nozzle formed to the printing head while moving back and forth on the printing medium in the direction orthogonal to the direction of conveying the printing medium so that small ink dots are formed on the printing medium. If the carriage is provided with ink cartridges of four colors, i.e., black, yellow, magenta, and cyan, and their each corresponding printing heads, full-color printing becomes easily possible in addition to monochrome printing.
With an inkjet printer of a type using no carriage but a printing head of the length same as the width of the printing medium, there is no need to move the printing head in the width direction of the printing medium. This accordingly enables printing with a so-called single path, thereby favorably leading to high-speed printing as can be with laser printers. Note here that the inkjet printer of the former type is generally referred to as “multi-path (serial) inkjet printer”, and the ink jet printer of the latter type as “line-head inkjet printer”.
A line-head inkjet printer is often configured to place a printing medium on a conveyor belt for conveying. With such a configuration of placing a printing medium on a conveyor belt for conveying, to achieve printing with high image quality through ejection of a liquid ink onto an incoming printing medium from the printing head, there needs to detect the position of the printing medium with good accuracy. For this purpose, generally, the conveyor belt is provided with a mark for detection of the movement status, i.e., movement amount and speed such as linear scale. The mark is read by an encoder so that the position of the conveyor belt is detected, and from the detected position of the conveyor belt, the position of a printing medium is detected. For such detection, however, there needs to set a reference position for the conveyor belt for use as a position reference for the printing medium because the conveyor belt is generally endless. In consideration thereof, with an inkjet printer described in JP-A-2006-96429, a conveyor belt is provided with a tab for use as a position reference of the conveyor belt through detection thereof by a sensor, and control is so exercised as to place a printing medium not on the seam of the belt.
The problem with the previous technology typified by JP-A-2006-96429 is that there needs to include two sensors, i.e., a sensor for detecting the movement status of the conveyor belt, and a sensor for detecting the reference position of the conveyor belt, thereby complicating the configuration and increasing the cost.